1. Field of the Invention
The present invention relates to a magnetic information reproducing apparatus which reads magnetic information from a magnetic recording part or the like provided on a photographic film.
2. Description of Related Art
It has been widely practiced to form a magnetic recording-and-reproducing area with a magnetic matter on a tape, like in the case of an audio tape, and to record or reproduce magnetic information on or from the tape by using an apparatus having a magnetic head.
Meanwhile, a photographic system which has recently become popular and commercialized is arranged to provide a film with a magnetic recording-and-reproducing area by forming a magnetic layer on the film, to provide a camera or a film scanner with a magnetic head, to write information about the date of photo-taking, a shutter speed, etc., into the magnetic recording-and-reproducing area with the magnetic head, and to read, as necessary, the information from the magnetic recording-and-reproducing area with the magnetic head.
Generally, a magnetic head and a magnetic reproducing circuit are highly prone to be affected by noises of varied kinds. When a strong magnetic field is inflicted from outside while a reproducing apparatus is in process of magnetic reproduction, for example, signals are apt to be erroneously reproduced. Therefore, some cameras have been developed not to be affected by such noises, as disclosed, for example, in Japanese Laid-Open Patent Application No. HEI 6-35059 and Japanese Laid-Open Utility Model Application No. HEI 6-28850.
Further, it has sometimes been difficult to read magnetic information with a magnetic head as the magnetic head is affected by an electromagnetic noise generated by a motor which is used as a drive source for transporting a magnetic recording medium. To solve this problem, some cameras have been developed against such a noise, as disclosed, for example, in Japanese Laid-Open Patent Application No. HEI 4-26832. According to the disclosure, the camera is provided with a magnetic head for recording or reproducing photo-taking information or the like on or from a film having a magnetic recording part, a driving motor is disposed within a take-up spool, and a shield case which is made of iron is disposed around the outer circumference of a motor yoke of the driving motor in a state of being insulated from the motor yoke. With the camera arranged in this manner, even if an electromagnetic noise generated by the rotation of the motor leaks from the motor yoke, the shield case prevents the magnetic head from being affected by the noise. The electromagnetic noise is prevented more effectively with copper plating applied to the shield case.
Other known examples of arrangement against the electromagnetic noises caused by motors were disclosed, for example, in Japanese Patent No. 2623468, Japanese Laid-Open Patent Application No. HEI 9-113986, etc. In these known examples, the adverse effect of such a noise is prevented by suitably arranging the layout of the motor and the magnetic head.
As mentioned above, the arrangements disclosed in Japanese Laid-Open Patent Application No. HEI 6-35059 and Japanese Laid-Open Utility Model Application No. HEI 6-28850 are developed against the adverse effect of a strong external magnetic field on the reproducing apparatus. The arrangements disclosed in Japanese Laid-Open Patent Application No. HEI 4-26832, Japanese Patent No. 2623468 and Japanese Laid-Open Patent Application No. HEI 9-113986 are developed against the adverse effect of an electromagnetic noise generated by a motor on the magnetic head.
In actuality, however, the magnetic head of a magnetic information reproducing apparatus receives also electromagnetic noise generated by a battery used as a power supply for a transport motor besides the above-stated strong external magnetic field and the noise generated by the motor. The magnetic head thus sometimes performs an erroneous reproducing action due to the noise generated by the battery. More specifically, when a current is allowed to flow from a battery to a motor having a brush to drive (rotate) the motor, the current varies according to the phase of the shaft of the motor. Then, a change in magnetic field is brought about by the battery itself to affect the magnetic head.